Optical windows can be used to protect the face and eyes of a wearer from spatter, debris, and other projectiles that can cause harm to a wearer's face and eyes while still allowing the wearer to see clearly through the window. For example, helmets, face masks, goggles, windshields and the like are used in a variety of different environments, such as in racing (e.g., horse, auto, motorcycle, bike, etc.), workshops and laboratories, and surgical environments, to name but a few. In many of these environments, spatter and other debris can accrue on the eyewear, thereby occluding the field of vision for a user. Moreover, in addition to the issues caused by a soiled window, glare caused by the reflections of light off the window can also inhibit the wearer's ability to see clearly. In many of these environments, such visual imparities can present serious health and safety issues. For instance, in environments that involve high speed travel (e.g., racing), or complicated technical endeavors (medical procedures), visual obstructions caused by spatter or glare can have a negative impact on performance and result in untimely accidents or errors that can pose serious risks.
Regarding visibility issues caused by spatter and debris, it is not always possible or effective to simply wipe away the spatter to clear the field of vision. For instance, racers and surgeons frequently will not have a free hand or a towel available to wipe their eyewear clean, and even if they did, such wiping could still smear or leave behind residue that could occlude the field of vision. One technique for helping such individuals clear their field of vision involves providing tear-off lenses on the eye protector. In this way, wearers can remove an outer-most tear-off lens layer when it becomes soiled, thereby exposing a clean layer underneath to provide a clear field of vision. More tear-off lenses on the eyewear provide more opportunities for the wearer to clear their field of vision; however, each layer in a tear-off lens stack can further contribute to the glare generated.
Glare and reflectance off an optical surface can be reduced by employing anti-reflective coating (AR coating) on the optical surface. AR coatings typically consist of many transparent thin film structures that have alternating layers of contrasting refractive index. In this sense, “thin films” is not a relative term, but instead refers to films that have a thickness that is on the order of half the wavelength of visible light, or less. For instance, thin films may refer to films having a thickness of between 50 nm to 250 nm (0.05 microns to 0.25 microns) or even thinner. The thin film layers are chosen to make up the AR coating are selected to produce destructive interference in the beams reflected from the surfaces and constructive interference in the corresponding transmitted beams. While these AR coatings can be effective in reducing reflections, they are also expensive to produce and apply. For example, the thin film AR coatings are typically applied either in a vacuum environment or by spin coating. However, vacuum environments for processing are very expensive and preclude commercial use of large area disposable lenses. And spin coating is suitable for application on small, round substrates having an area less than one square foot, but is not viable for web processing. In addition, thin film AR coatings are subject to color shift, such that when viewed at angles, the AR coatings tend to provide a colored hue or tint (e.g., a violet hue), which may undesirably take away from viewing in environments where clear vision is paramount. Accordingly, using AR coatings to reduce glare on optical webs or products formed therefrom, on laminated material such as tear-off lens stacks, or on other disposable materials such as disposable shields and windows, is not a cost effective technique for reducing reflections.